Seoul, South Korea ? A North Korean diplomat confirmed that his country had shut down its sole operating nuclear reactor after receiving an initial shipment of oil aid and said U.N. inspectors would start verifying the closure on Sunday.

If confirmed by the U.N. inspection team, the shutdown would be the North’s first step in nearly five years toward denuclearization, one that comes after lengthy international talks.

“Immediately after the arrival of the first heavy fuel oil, the facilities were shut down and the (International Atomic Energy Agency) personnel will verify that maybe by now, or from today in Korea,” Kim Myong Gil, minister at the North’s mission to the United Nations in New York, told The Associated Press by telephone.

Saturday’s delivery of 6,200 tons of heavy fuel oil from South Korea was the first of 50,000 tons promised to the North in exchange for shutting down its reactor in a deal with the United States, China, Japan, South Korea and Russia. Pyongyang will eventually get 1 million tons of oil and other financial and political concessions.

After tortuous negotiations and delays – during which the North argued its nuclear program was needed for self-defense – the reclusive regime said earlier this month that once it received the oil shipment, it would consider halting its reactor.

In Washington, the State Department said Saturday that North Korea had told the United States the reactor had been shut down, hours after the oil arrived in port.

“We welcome this development and look forward to the verification and monitoring of this shutdown by the International Atomic Energy Agency team,” State Department spokesman Sean McCormack said in a statement.

South Korea praised the North’s move as “the first step toward translating the North’s commitment to denuclearization into action.” In a statement by Foreign Ministry spokesman Cho Hee-yong, Seoul called on Pyongyang to “speed up the implementation of the next phase” of its commitment to disarm.

The 10-member IAEA team arrived in the North Korean capital Saturday afternoon. Team chief Adel Tolba said the inspectors would stay in North Korea as long as needed to complete their work at the Yongbyon plutonium-producing reactor, located about 60 miles northeast of Pyongyang.